History and Overview of Rotating Wing Aircraft Photo by Paolo Rosa Produced by the American Helicopter Society (AHS) International STEM Committee: www.vtol.org/stem Free to distribute with attribution

History of Rotorcraft Definition of Rotorcraft Any flying machine using rotating wings to provide lift, propulsion, and control that enable vertical flight and hover Rotating wings provide propulsion, but negligible lift and control. Rotating wings provide lift, propulsion, control at same time.

History of Rotorcraft Two key configurations developed in parallel Autogiro Close to helicopter, uses many of same mechanical feature Cannot hover Unpowered rotor Helicopter Powered rotor Many configurations have been developed Autogiros flew first! Autogiro innovations enabled development of first helicopters

Autogyro – How it Works Lift Thrust Unpowered Rotor that Spins Due to Wind Blowing Through Rotor Like a Wind Turbine Relative Wind No Need for Anti-Torque Since Not Driven By an Engine Fixed to the Fuselage Thrust Control Surfaces

Autogyro – How it Works Kind of like parasailing, except rotor provides lift in addition to drag.

Helicopter – How it Works Powered Rotor Equal and opposite torque applied to rotor acts on fuselage Tail Rotor Thrust Rotor Thrust Main Rotor Drive Shaft Tail Boom Cockpit Tail Rotor Engine, Fuel, Transmission, etc. Landing Skids Controls

Helicopter – Need for Anti-Torque Engine fixed on body – exerts torque on rotor shaft Rotor shaft exerts equal and opposite torque on body Many configurations created around anti-torque problem Autogyros, tip jets, tip propellers, tandem helicopters, tilt wings, tilt rotors, synchcopter -T T

Basic Rotor Controls Flap and Lag Hinges Pitch Bearing Rotor Control Servos Pitch Link Swashplate Red = Rotating Blue = Fixed

Basic Rotor Controls Cyclic control Collective Control Changes pitch sinusoidally of all blades around azimuth angle (blade rotation angle) Accomplished by tilting swashplate side to side on gimbal Collective Control Increases/decreases pitch on all blades at all azimuthal locations Accomplished by moving swashplate up and down rotor shaft Blade azimuth angle ψ

Key Problems in Early Rotorcraft Development Understanding basic aerodynamics of vertical flight Amount of power to produce fixed amount of lift was unknown First significant application of aerodynamic theory to helicopter rotors came about in the early 1920s Lack of a suitable engine Not until the mid-1920s that engines with sufficient power and with high power to weight ratios suitable for vertical flight became widely available Minimizing weight Early engines made of case iron – too heavy! Aluminum not cheap enough for use on aircraft until 1920

Key Problems in Early Rotorcraft Development Counteracting rotor torque reaction Tail rotor to counter torque reaction and provide directional control not used on most early designs Igor Sikorsky was the first to successfully use the tail rotor in the single rotor helicopter configuration we know today. Providing stability and control Primary concern was to devise a means of defeating the unequal lift produced on the blades advancing into and retreating from the relative wind when in forward flight Problems overcome only with articulated rotor and cyclic pitch control Conquering high vibrations Vibration was source of many mechanical failures of the rotor and airframe Reflected an insufficient understanding of the dynamic and aerodynamic behavior of rotating-wings

History of Rotorcraft

Early Concepts Chinese Top – 400 B.C.

Early Concepts DaVinci - 1493 Leonardo da Vinci credited with first idea for vertical flight Oversized Archimedes water screw Airscrew consisted of platform with metal helical screw Propellers made of starched linen, frame made of wire Just a sketch

Enabling Devices Lomonosov - 1754 Russian, Mikhail V. Lomonosov Very first self-propelled model of a lifting airscrew flown Coaxial rotor system, spring-driven device Flown freely and climbed to good altitude Intended for lifting thermometers and other instruments into the air

Enabling Devices Phillips – 1840’s, D’Amecourt – 1860’s Horatio Phillips, 1840’s Constructed first steam driven vertical flight machine Steam generated by mini-boiler ejected at blade tips First time rotorcraft flew under engine power Ponton D’Amecourt, 1860’s Also designed, built, and flew a a number of small steam powered helicopter models Coaxial rotors Pictured on right

Enabling Devices Bright - 1859 Henry Bright, Englishman First helicopter patent granted by the British Patent Office Two counter-rotating coaxial two-bladed rotors Mounted on a vertical shaft

Enabling Devices Achenbach - 1874 Wilheim Achenbach, German Single rotor concept First side thrusting tail rotor to counteract main rotor torque

Enabling Devices Forlanini - 1878 Enrico Forlanini, Italian Steam driven helicopter model, dual counter-rotating propellers Forced superheated steam to a high pressure in a small metal sphere Flew 40 ft for 20 sec

Early Contraptions Cornu - 1907 Paul Cornu, French Bicycle Maker Vertical flight machine carried human off ground for the first time Dual rotor, 24 HP gas engine, belt-driven

Early Contraptions Breguet - 1907 Louis and Jacques Breguet, French Scientists Quad-Rotor gyroplane, 40-hp engine, Briefly carried a pilot off the ground

Early Contraptions Sikorsky - 1909 Igor Sikorsky, Russian Prototype coaxial nonpiloted helicopter Did not fly due to vibration problems and lack of power

Early Contraptions Yurev - 1912 B.N. Yuriev, Russian Developed single main rotor helicopter Included collective pitch, cyclic pitch, and tail rotor Aircraft never flew properly due to lack of power

Early Contraptions Ellehammer - 1914 Jacob Ellehammer, Danish Coaxial rotor helicopter Short blades attached to 2 large circular aluminum rings Top ring like a parachute for failures Aircraft made short hops off the ground

Early Contraptions Petroczy – 1920 Stephan Petroczy, Austrian, assisted by Theodore Von Karman Build and flew coaxial rotor helicopter Pilot-Observer positioned over the rotors, inflated bags for landing gear Powered by 3 rotary engines Machine only flew tethered to ground

Early Contraptions Berliner – 1909 to 1920 Emile and Henry Berliner, father and son from United States Developed coaxial and side-by-side rotor helicopters First to observe power required decreases when entering forward flight Side-by-side aircraft: twisted rotor blades Side-by-side aircraft control: Differential shaft tilt, wings in slipstream

Early Contraptions Brennan – 1920 Louis Brennan, English Single 2 bladed rotor Rotor driven by propellers on blade tips (no anti-torque needed)‏ Control achieved with servo flaps inboard on rotor Machine flew successfully inside a balloon shed, crashed on Flight 7

Early Contraptions Pescara – 1920’s Raul Pescara, Argentinan working in spain and france Coaxial helicopter with biplane-type rotors First to use cyclic blade pitch Aircraft achieved short uncontrolled flights

Early Contraptions Von Baumhauer – 1924 A.G. Von Baumhauer, Dutch Single main rotor helicopter Collective pitch, cyclic pitch See-saw teetering rotor Main and tail rotors not connected – difficult directional control Machine made several short semi-controlled hops off ground

Autogyro – First Flight - 1923 Juan de la Cierva, Spaniard Hinged Blades, standard fixed wing aircraft controls in rotor slipstream Low speed control difficult, lack of dynamic pressure Required about a 50 ft ground run

Autogyro – Cyclic Pitch - 1931 E. Burke Wilford, American First rigid rotor to fly First to use cyclic blade pitch

Autogyro – Direct Control - 1932 Juan de la Cierva, Britain Rotor mounted so shaft can be tilted for control Led to elimination of ailerons and stub wings.

Autogyro – Coming Back Jay Carter, United States “Personal Air Vehicle” 2-bladed rotor, pusher propeller, tip weights on blades for jump take-off Rotor slowed in forward flight for reduced drag

Early Helicopters Bothezat – 1922 Georges de Bothezat, United States Quad-rotor, 6 bladed rotors Controlled by collective, differential collective, and cyclic pitch Called the “Flying Octopus” Flew many times successfully at low altitude and low speed

Early Helicopters Oemichen – 1924 Etienne Oemichen, French Quad-rotor Helicopter Won FAI award for the first helicopter to fly a 1 km standard circuit Stable and somewhat maneuverable machine

Early Helicopters d’Ascanio – 1930 Corradino d’Ascanio, Italy Built and flew successful coaxial helicopter Two bladed rotors, flapping hinges, collective and cyclic pitch Servo tab control on blades Small propellers on fuselage used for additional pitch control

Early Helicopters Bleeker – 1930 Maitland Bleeker, United States 4-Bladed single rotor helicopter Followed work of Brennan, rotor powered By props on blade tips Servo tab control on blades

Early Helicopters Florine – 1933 Nicolas Florine, Belgium Built and flew one of the first tandem rotor helicopters Rotors spun in same direction, but tilted differentially for anti-torque Flew for 9 minutes to an altitude of 15 ft

Early Helicopters Focke – 1936 Henrich Focke, German Built and flew successful side-by-side rotor helicopter Three bladed rotors, flap and lag hinges Longitudinal control via swashplate on rotors Lateral control via differential collective on rotors First helicopter to demonstrate autorotation

Early Helicopters Weir Company – 1938 Weir Company, Scotland Side-by-Side rotor helicopter Cyclic pitch on blades No collective pitch, altitude controlled by rotor RPM Small propellers on fuselage used for additional pitch control

Early Helicopters Flettner – 1939 Antoine Flettner, German First synchcopter helicopter First to show autorotation and return to powered flight

Early Helicopters Sikorsky – 1940 Igor Sikorsky, United States Successful single main rotor helicopter Flapping hinges and cyclic pitch Original machine had 3 small tail rotors, later reduced to one Considered the first practical helicopter

Rotorcraft Configurations

Single Main Rotor Helicopter

Tandem Rotor Helcopter

Synchcopter

Tilt Wing Aircraft

Tilt Rotor Aircraft

Tip Jet Driven Rotorcraft

Compound Helicopter McDonnell XV –1 Tip jet driven main rotor, very noisy Pusher propellers Large wings First rotorcraft to fly to 200 mph

Compound Helicopter Tip jet driven main rotor, very noisy

Compound Helicopter

Compound Helicopters

Compound Helicopter

Compound Helicopter

Compound Helicopter

Compound Helicopter

Compound Helicopter

Compound Helicopter

Compound Helicopter Sikorsky X2 Technology Demonstrator Achieved helicopter speed record of 252 kts (290 mph) on 15 September 2010 Retired on 14 July 2011 after 23 successful flights Led to development of S-97 Raider high-speed scout/attack helicopter